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Exhaust and roller rockers

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Exhaust and roller rockers

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Old 03-15-2019, 03:34 AM
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Default Exhaust and roller rockers

I have a pair of 2002 350 mag MPI's in my Formula. I recently purchased 2 sets of IMCO powerflows and tails from a boat buddy. Do I need to worry about snapping bolts like on a car manifold when I remove the stock ones? And i really want to install roller rockers while the exhaust is off, which ones should i get? Thanks!
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Old 03-15-2019, 05:26 AM
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All you will get with roller rockers is a little free'd up power, maybe a few horses at full throttle. But they are a step toward a cam or other upgrade. So make your best choice.
Best bang for my buck on the rockers was Scorpion four years ago, although I like the ones at Comp Cams, Crane or Harland Sharpe too. Here's a good link to some rocker information. https://www.enginebuildermag.com/201...e-rocker-arms/
Don't buy no-name offshore stuff. And those roller tip things are not full roller so I wouldn't get them.
Test fit the valve covers while putting in the rockers. If you have Mercruiser center bolt valve covers you can remove some of the internal baffling with aircraft shears. Watch out for clearance to your Powerflow exhaust for the valve covers. I bought tall valve covers for my 383 rockers and it's a chore to put them on and off without removing my (EMI Thunder) exhaust manifolds. I sometimes wish for short covers like my 87 had. That's the engine that I did the internal valve cover trimming on.
Your exhaust mani bolts won't likely be as stuck as car engine stuff gets. If they don't come loose right away you might try running the engine for a few minutes to heat cycle it a bit. Also you can put a socket on a breaker bar and work each bolt counter clockwise and clockwise a little at a time til the bolts turn.
While it's apart clean the bolt holes. you'll need SAE thread chasers. Don't use taps, just thread chasers. They remove corrosion without cutting away your metal.
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Last edited by NHGuy; 03-15-2019 at 05:28 AM.
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Old 03-15-2019, 12:53 PM
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The exhaust bolts should not be bad to get out. I doubt you'll have an issue with any bolts snapping.
Going to roller rockers is a waste of money on your engines and will gain nothing. Not to mention, they might not clear your valve covers.
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Old 03-15-2019, 03:18 PM
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Originally Posted by Griff View Post
The exhaust bolts should not be bad to get out. I doubt you'll have an issue with any bolts snapping.
Going to roller rockers is a waste of money on your engines and will gain nothing. Not to mention, they might not clear your valve covers.
I did read somewhere that they wouldnt clear. It's just an Idea because I run WOT alot. More now this year that I have a slip on Lake Michigan.
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Old 03-15-2019, 03:38 PM
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I like the Comp pro magnums. The gain is in the friction you eliminate. Add push rods to the shopping list and studs. I have pulled covers on a stock motor to find the pivot cup on some of the stamped steel rockers was bright blue from heat. I think the oil was shooting over the rocker at high rpm. It’s just another corner Merc. Cuts on the black motors
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Old 03-15-2019, 03:40 PM
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Iíd agree that the juice isnít worth the squeeze on the roller rockers. The factory stamped units are much more forgiving in set up than roller rockers, so until you go for bigger power with new heads I wouldnít mess with whatís working now. They may even compromise longevity if the geometry is off.
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Old 03-15-2019, 03:48 PM
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Originally Posted by ph1971 View Post
I like the Comp pro magnums. The gain is in the friction you eliminate. Add push rods to the shopping list and studs. I have pulled covers on a stock motor to find the pivot cup on some of the stamped steel rockers was bright blue from heat. I think the oil was shooting over the rocker at high rpm. Itís just another corner Merc. Cuts on the black motors
my engines have 475 hours on them, my plans include pulling the valve covers and installing new gaskets (starting to leak) borescope the cylinders and do compression/leak down tests. Anything else I should check for?
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Old 03-15-2019, 04:26 PM
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Oil temp gauges. Leaking gaskets can be the result of overheated oil. Running hard has a limit with stock oil coolers.
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Old 03-15-2019, 05:29 PM
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No gain unless youíre adding lift via rocker ratio.
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Old 03-15-2019, 06:39 PM
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Fwiw, I put the Comp Cams ultra endurance rockers on my 502 and picked up maybe 50rpm on top, spent $300 in valve covers in doing so, twisted my back in the bilge for an afternoon, and are more noisy than stock.

You can pop a valve valve cover and see if the ball/fulcrum looks burnt, otherwise spend that same money on beer and have a better result.
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